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Members of Ammocrypta (Percidae), known as sand darters, have experienced widespread population declines, yet little is known regarding their ecology and life history. The purpose of this study was to examine life history traits and provide much needed information on the western sand darter (Ammocrypta clara) from a population in Northeast Arkansas. The Strawberry, Black, and Current rivers were sampled by seine or trawl from Jun. 2007–Sep. 2008. Life history traits were examined on 379 specimens. Mean size was 42.9 mm standard length (max. 50 km SL) and males and females reached maturity between 35–40 mm SL. The spawning season was May to Aug. and mean monthly gonadosomatic index (GSI) ranged from 3.4–4.9%. Gravid females averaged 57 eggs per clutch and mean egg size was 0.79 mm across mature, ripening, and ripe stages. Significant relationships existed between female standard length, ovarian mass, and clutch size. Observation of captive specimens in aquaria revealed crepuscular spawning with eggs (mean = 1.22 mm) buried singly in the sand and clutches released over short periods of time (hours to days). Overall, A. clara from Arkansas possessed several life history traits that differed from data reported for A. clara in Wisconsin and other species of Ammocrypta. We found that fish were smaller in size, had lower GSI values, smaller clutch sizes, and smaller egg sizes compared to other Ammocrypta, reflecting potentially important life history trade-offs between size and age (longevity) and the relationship among GSI, clutch size, and egg size.
Excess sediment in streams (measured as embeddedness), whether from natural or anthropogenic sources, has adverse effects on the biota that inhabit these systems. Aquatic macroinvertebrates exhibit reductions in diversity and abundance, which in turn leads to a reduction in the availability and quality of food for their fish predators; however, macroinvertebrate communities were not significantly different from one another. The predator-prey relationship between mottled sculpin (Cottus bairdii) and macroinvertebrates was examined in four headwater streams with differing embeddedness levels (15% and 35%) in Garrett County, MD. Embeddedness was not different enough to cause a shift in the macroinvertebrate community. Sculpin in both streams showed a pattern in which larger individuals were consuming larger prey items, and in turn more energy, in certain seasons. This pattern was evident in the summer, autumn, and winter for the 15% embedded streams and spring and autumn for the 35% embedded streams. Compositional analysis revealed that sculpin from the lower embeddedness level were consuming ephemeropterans regardless of their abundance, and sculpin from the higher sediment level preferred chironomids. A reduction in body condition was found at one of the 35% embedded sites, possibly due to consuming smaller, lower energy prey. It may be possible that increasing embeddedness levels are not changing the macroinvertebrate community but might restrict benthic fish access to valuable prey resources.
Assessing the population status and dynamics of species is an important component of monitoring efforts aimed at improving understanding of relationships between freshwater mussels (Bivalvia:Unionidae) and their environment. Most freshwater mussel population assessments are conducted using raw count (density, abundance) or presence/absence data but relatively few studies account for potential biases associated with incomplete detection of individuals or species during sampling. We conducted a capture-mark-recapture study over 7 y to assess survival and recapture probabilities of three federally endangered freshwater mussels in a small southeastern U.S. stream. Although similar numbers of mussels were collected among sampling occasions, only a small proportion of the individuals present within the sampling site were collected on any given occasion. Mean apparent survival was 0.81 and did not vary among species or among years. Modeling results indicated that recapture probabilities varied among species, through time, and among individuals as a function of shell length. Recapture probabilities for Pleurobema pyriforme and Medionidus penicillatus increased with increased shell length, whereas recapture probabilities for Hamiota subangulata decreased with increasing shell length. Under the generally accepted assumption of constant recapture among sampling occasions, apparent survival estimates ranged from 0.89 to 0.99 among the three species and decreased for H. subangulata with increased shell length. Our study demonstrates that failure to account for incomplete recapture of freshwater mussels could bias inferences regarding the status and trajectory of mussel populations, which may in turn result in the implementation of ineffective management and conservation strategies.
Muskrats (Ondatra zibethicus) are known to prey on freshwater bivalves (mussels and clams) and can negatively impact imperiled mussel species. However, factors that influence muskrat predation on bivalves are poorly understood. We evaluated the feeding ecology of muskrats in the Green River, Kentucky, by using stable isotope analysis of muskrat hair samples and by monitoring bivalve shell deposition at muskrat middens. Bayesian mixing-model analysis of stable isotope δ15N and δ13C ratios revealed that the median muskrat biomass derived from bivalves was 51.4% (5th and 95th percentiles were 39.1 to 63.4%, respectively), a much higher dietary proportion than previously reported. Shell depositions by muskrats at middens decreased with the availability of seasonal emergent vegetation, suggesting that the consumption of animal matter is in response to a scarcity of plant foods, perhaps exacerbated by the altered flow regimes on the Green River. Our results add to the growing body of evidence that muskrats have the potential to impact mussel population growth and recovery in some environments.
Restoration of wetland ecosystems has typically focused on hydrology, soil, and vegetation; taking an, “If you build it, they will come” strategy for the recovery of wetland fauna. We tested this assumption by quantifying mammal richness and abundance in recently restored and nonmitigated reference wetland habitats to determine if mammalian community composition varies with wetland condition. Our study consisted of live trapping and infrared photography at three restored and three reference (“natural”) wetland sites in Northeastern Ohio. After 3000 potential trap nights and 120 potential camera nights, we documented the presence of nine species and nearly 300 unique individuals in reference and restored wetlands. We found no significant differences in mammalian richness, abundance, or species composition between reference and restored wetlands; however, mammal abundance in terms of individual captures was 62% higher in restored wetland patches (n = 194) than in reference wetlands (n = 104). Restored wetlands – if managed correctly – can harbor mammalian communities as rich as those found in nonmitigated wetland habitats. Our results support the “Field of Dreams” hypothesis which suggests, among other things, that if the necessary physical conditions are present then desired fauna will subsequently colonize the patch. For small to midsized mammals in our study area, this appears to be the case.
Stable coexistence of ecologically similar species is often a complicated phenomenon involving a synergy of biotic and abiotic factors. We investigated competitive interactions and small scale division of space in the closely related vole species Microtus montanus and Microtus longicaudus, which co- occur across the Greater Yellowstone Ecosystem (GYE) in the Rocky Mountains. We directly manipulated in situ populations of these species in two habitat types over three consecutive years. We confirmed previously described habitat associations of the study species: M. montanus was most abundant in open grassy meadows; M. longicaudus was most abundant in ecotonal areas with greater woody vegetation cover. Additionally, removal experiments conducted in both habitat types revealed a habitat-dependent competitive interaction between species: M. montanus excluded M. longicaudus from resource-rich meadows; M. longicaudus was limited to patchy ecotonal habitats that M. montanus was not observed to colonize. We did not observe an effect of the experimental treatment on either species' body mass. The outcome of the asymmetric competition between these species is influenced by local environmental conditions and enables their coexistence in the GYE.
We isolated, amplified, and sequenced the mtDNA from insect fragments found in the feces of big brown bats (Eptesicus fuscus) caught in apple orchards, to determine whether the bats were consuming prey of economic interest, especially common pests of apples. Comparison of sequences to those in a reference database (Barcode of Life Database) allowed identification of 58 sequences from 40 bats to the level of family, genus, or species; 40 (69%) of the 58 sequences of insects matched to species, 6 (10%) to only genus, and 12 (21%) to only family. Forty-nine (84%) of the 58 matches, from 34 (85%) of the 40 bats, were to taxa within the order Coleoptera and most represented taxa within the family Carabidae; other orders included Diptera, Ephemeroptera, and Hymenoptera. Eighteen different species were identified, including several important pests, such as various mosquitoes (Aedes), the spotted cucumber beetle (Diabrotica undecimpunctata), and pavement ants (Tetramorium caespitum), although no pests specific to apples were discovered.
Coyotes (Canis latrans) have expanded to live in urban areas with limited natural habitat. A year long coyote howl survey combined with geospatial information systems (GIS) was applied to locate populations within a metropolitan region, to determine the habitats where coyotes most frequently occur, and to estimate group sizes within this urbanized region. Surveys were conducted along the perimeters of natural areas and urban-residential communities. Coyote response rates varied among parks, they increased during the dispersal season relative to the breeding and pup-rearing seasons, and responses increased when broadcasts were performed closer to sunset and/or later at night as well as when temperatures were low and the moon more visible. Group sizes were estimated to be between five and 13 individuals within the parks studied, although almost half of all responses originated from outside park boundaries. In the residential areas, natural land cover was present and the areas from which coyotes were predicted to have called contained a greater proportion of natural cover than the region as a whole but variation in land cover was much greater outside parks. Overall, howl surveys allowed for an inexpensive monitoring of coyotes over large areas in urban-park environments.
Although understanding natural mortality rates of ungulate populations is essential for effective management, published data on adult survival from unharvested pronghorn (Antilocapra americana) populations in the Northern Great Plains is limited. We estimated seasonal adult survival rates and cause-specific mortality of an unharvested pronghorn population in Custer State Park, S.D. We assessed the relative importance of sex, age, year, and season in explaining pronghorn survival rates using an information-theoretic approach. We captured and radio-collared 26 male and 24 female adult pronghorn from fall 2005 through spring 2008. We observed higher predation rates and lower survival of adult pronghorn in CSP compared to other populations in the region, but similar to the pronghorn population in Yellowstone National Park. We documented 23 deaths (10 females, 13 males) of the 50 radio-collared pronghorn from Nov. 2005–Nov. 2008. Predation by mountain lions (Puma concolor) and coyotes (Canis latrans) accounted for 69.5% of all mortalities. The season model received the greatest support although there also was strong support for the season × sex model. Seasonal survival for males and females was >0.90 for the winter-grouping and breeding seasons but fell to 0.791(95% CI 0.644–0.887) and 0.837 (95% CI 0.706–0.916) for females and males, respectively, during the small group – parturition season. A dense predator population, as well as a higher vulnerability to predation when pronghorn are solitary or in small groups, may explain the lower survival during these time periods. If population estimates fall below management goals, management actions aimed at reducing predator cover may be beneficial to adult pronghorn. Managers of pronghorn populations near forested and rugged areas and that are sympatric with dense predator populations should consider adult survival may be lower than observed in Great Plains populations.
Native grasses and forbs were once dominant in tallgrass prairies, but nonnative plants have largely replaced natives in most grassland of Illinois. Ample evidence indicates that white-tailed deer (Odocoileus virginianus) have a strong impact on native forests and prairie, but we know little about their impact on nonnative grasslands. This study tested the hypothesis that foraging by deer on native forbs and woody plants increases the dominance of introduced grasses as succession proceeds in old fields of central Illinois. We tested that hypothesis using fencing that excluded deer, but not other herbivores, from replicated plots in three old fields at different successional stages. The composition of the plant community changed rapidly in early succession and showed relatively little effect of deer, other than slowing the invasion by woody plants. In mid- and late successional fields, however, fenced plots had higher relative abundance of native forbs, particularly goldenrod (Solidago spp.), and lower relative abundance of introduced perennial grasses than did control plots. Thus, deer facilitated introduced perennial grasses and inhibited native forbs and woody plants in old fields, thereby delaying succession to deciduous forest.
A study over time provides a unique approach to investigate if landscape-environmental conditions can explain community resistance to invasion by nonnative plants in protected forest patches. This study investigated overall and intra-forest spatial patterns of change in nonnative Lonicera maackii (Amur honeysuckle) after 18 y in a 5.2 ha mature deciduous forest in southwestern Ohio. Changes in height-class abundances were measured in 60 permanent plots and mapped using GIS. Amur honeysuckle density increased from 3361 to 5472 individuals/ha (62.8%), but increases and decreases occurred at different sample plots. Greatest increases were for individuals <1 m (86.3%). A repeated measures MANOVA confirmed the significant effects of time (1992–2010) for total density, density of individuals >1 and <1 m, and mean height, but the decrease in mean height (1.44 to 1.30 m) was not significant in the univariate analysis. Moran's I statistic calculations documented nonsignificant spatial autocorrelations among plots, but landscape-environmental attributes have weak and mostly non-significant relationships with the change in honeysuckle densities among the plots. Management practices can decrease propagule pressure along edges and reduce the establishment of small individuals in the interior, but Amur honeysuckle is likely to remain as a naturalized understory shrub that responds to spatially fluctuating resources in this mature forest fragment.
In this study, we assessed growth response of Quercus buckleyi (Texas red oak), a current codominant deciduous oak species in central Texas woodlands, to changes in competition, fire, and climate over time to evaluate factors related to documented regional decline of this species. For this analysis, we collected 372 tree slabs of Texas red oaks from the woodlands of the Balcones Canyonlands National Wildlife Refuge near Austin, Texas, from which we aged fire scars and measured tree-ring widths to calculate basal area increment and ring-width indices. To determine canopy conditions of these trees over time, we used historical aerial photos from 1937 to 2004 acquired approximately every 15 y to evaluate changes in woody vegetation cover for the locations of the trees sampled. Our results showed that trees affected by loss of local woody vegetation cover, as evaluated by the aerial photographs, and fire had higher average basal area increment than trees without fire evidence and loss of cover. These differences were significant when aspect and slope were added to the analysis. For climate, we found significant correlation between annual Palmer Drought Severity Indices and ring-width indices for the time interval of 1937–1978, but not after, indicative of potential recent decoupling between tree-ring changes and climate. We found drought to potentially be a major driver of community change in this system as it affects tree-ring response, fire, and mortality assessed from sampled trees.
Population restoration and reintroduction are critical aspects of many plant conservation efforts. However, factors affecting the earliest life stages, critical to the establishment of new individuals, are often poorly understood. I investigated the influence of seed characteristics and manipulations of the field environment on seedling emergence and growth in Asclepias meadii (Mead's milkweed), a federally threatened tallgrass prairie species. Seeds of known mass and maternal plant were reared in a greenhouse and also in experimental restoration plots with combinations of pre- planting soil disturbance and spring burning treatments. In both the greenhouse and field, seed mass was positively correlated with emergence but not growth. Maternal relationships with emergence and growth were observed in the greenhouse but were generally undetectable in the field. Lower emergence was associated with field plot soil disturbance and burning, although there was no statistically significant effect of either treatment. Seedling growth did not appear to be affected by soil disturbance, but burning had a significant negative effect. Mass may be a useful metric for evaluating restoration seed stocks and the quality of seeds produced in maturing restoration populations. Pre-emergence manipulations of the restoration site did not facilitate emergence or growth and may have even been detrimental to restoration efforts. High survivorship of seedlings during their first year of growth and overwintering suggests that direct sowing of seeds into the field is an effective restoration technique for A. meadii.
Animals in many freshwater habitats are experiencing decreased recruitment due to declines in reproductive health. Both subspecies of a long-lived aquatic salamander, (Cryptobranchus alleganiensis alleganiensis and C. a. bishopi) have experienced severe population declines characterized by low recruitment. For many states throughout their geographic range, captive propagation and translocation are the only remaining form of management given the severity of declines. These captive rearing programs should rely on techniques to assess male reproductive health, which are currently lacking. In this study, we compared the sperm health (motility, viability, and concentration) of male hellbenders from declining and stable populations. Sperm motility and viability were similar among populations, but sperm concentrations (sp/ml) were significantly lower in declining Missouri populations than in hellbenders from populations with higher recruitment in the southeast. Sperm from Ozark hellbenders was successfully cryopreserved but with low post thaw motilities. This method for assessing male reproductive health provides the first baseline comparative study among populations of this cryptic species in decline and has broad implications for use in monitoring male health across the distribution of the eastern hellbender.
Historically, melanistic fox squirrels have been found in Council Bluffs, Iowa, and along the Missouri River in Eastern Omaha, Nebraska. However, recent anecdotal observations suggest that the melanistic trait in fox squirrels is expanding westward into Omaha. Squirrels were surveyed in the autumn of 2010 and 2011 along transect lines within five major city sections and different habitat types; comparisons were made to a survey performed in 1973. Proportion of melanistic squirrels in Council Bluffs remained at levels similar to 1973 surveys (∼50% melanistic). Since 1973 melanistic fox squirrels have increased in Omaha, with a higher proportion of melanistic squirrels in northwest (7.4%) and northeast (7.6%) compared to southwest or southeast Omaha (4.6%). Melanistic squirrels were found in higher proportions in parks (12.1%) and residential (10.9%) habitats compared to business (6.1%), industrial (7.4%), or golf course (8.0%) habitats. Melanistic squirrels were also observed more frequently at colder temperatures than rufus squirrels. The results yielded significant variation in the percent of melanistic individuals in each section and suggest the proportion of melanistic individuals is increasing westward.